This invention relates to an electrochemical cell and in particular a structural frame for use in a zero gap electrochemical cell.
It is well established that various chemicals can be produced in an electrochemical cell containing an anode and a cathode. For example, alkali metal chlorates, such as sodium chlorate, have been formed electrolytically from a sodium chloride brine in cells without a separator positioned between the anode and the cathode.
When a separator, such as a liquid permeable asbestos or polytetrafluoroethylene diaphragm or a substantially liquid impervious ion exchange membrane, is used in a cell to electrolyze a sodium chloride brine, the electrochemical products will normally be gaseous chlorine, hydrogen gas and an aqueous solution containing sodium hydroxide.
For a number of years gaseous chlorine was produced in electrochemical cells wherein an asbestos diaphragm was interposed between finger-like, anodes and cathodes which were interleaved together. During the past several years it has become apparent that the use of a substantially liquid impermeable cation exchange membrane may be preferable to the more well established diaphragm in instances where a higher purity, for example a lower sodium chloride content, higher sodium hydroxide product is desired. It was found to be more convenient to fabricate ion exchange type electrochemical cells from relatively flat or planar sheets of ion exchange membrane rather than to interleave the membrane between the anode and cathode within the older finger-like cells used with asbestos diaphragms.
The newer, so-called flat plate electrochemical cells using a planar piece of ion exchange membrane to separate the anolyte from catholyte compartments also have a plurality of solid, liquid impervious frames adapted to support the anode on one side and the cathode on the opposite side. These frames have previously been constructed of materials such as metal and plastic, but neither of these materials has been found to be entirely satisfactory. In any electrochemical cell, including both monopolar and bipolar cells, there is a possibility that electrolyte may leak from within the cell to the exterior. In instances where such leakage has occurred in cells with iron or other ferrous type frames, it was found that the iron frame corroded or was itself electrolytically attacked. Plastic frames are not generally subject to the electrochemical attack, but are normally not resistant to the anolyte and/or catholyte within the cell under operating conditions for extended periods of time, for example, several years.
It is desired to provide a structural frame for use in zero gap electrochemical cells which would minimize the corrosion problems and would increase the relatively short useful life attendant with those frames used by the prior art.